Image processing apparatus, printing apparatus, and image processing method

ABSTRACT

In an image processing for printing a monochrome image, color deviation can be suppressed to print a favorable monochrome image. Specifically, the printing of a monochrome image is performed by using black ink in all of a color reproduction region (color gamut) including a gray axis and regions other than the gray axis. This avoids the use of C, M, and Y for the expression of the monochrome image to suppress the color deviation due to slight imbalance among amounts of three colors of inks.

This application is a divisional of U.S. patent application Ser. No.11/279,278, filed Apr. 11, 2006, the contents of which are incorporatedby reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image processing apparatus, aprinting apparatus, and an image processing method. In particular, thepresent invention relates to an image processing for determining anamount of color material for printing in generation of print data of amonochrome image.

2. Description of the Related Art

An ink jet printer image using a plurality of colors of inks as colormaterials has been widely known as an image formation apparatus foroutputting an image. An electro-photographic type printer has been alsoknown that uses toner as color material. These image formationapparatuses use three colors of cyan (C), magenta (M), and yellow (Y) orfour colors of cyan (C), magenta (M), yellow (Y), and black (K) torepresent various colors for printing by the subtractive color mixing.

The image formation as described above, however, often causes asituation where, when the printing is performed based on the respectivesignal values specifying amount of color materials such as C, M, and Yfor example, colors intended by these signal values cannot be reproducedfaithfully. For example, when sizes of dots formed by the respectivecolor materials are slightly different from one another on a printingmedium such as a paper, colors in a printed image composed of thecollection of these dots may be observed as the ones slightly dislocatedfrom intended one. This is caused, for example, when amounts (volumes)of ink droplets ejected from printing heads are slightly differentdepending on individual differences of heads or when the sizes of dotsof a latent image formed on a photosensitive material are slightlydifferent from one another in an electro-photographic type imageformation apparatus. The slight difference in dot size is also caused bya relation between the type of a printing medium and the characteristicof color material (e.g., ink, toner). Furthermore, the dot size alsochanges due to the change of these image formation apparatuses with age.

As described above, a phenomena in which an actual color of a printedimage is represented to have colors in a color space that are dislocatedfrom colors (position coordinates) intended by a color material signalmay be caused in many image formation apparatuses. Herein, such aphenomenon will be referred to as “color deviation”.

Conventionally, so-called calibration has been known as a method to copewith this color deviation. For example, patches are printed by a targetprinter. Then a color conversion table, a gamma correction table or thelike is changed or generated based on the colorimetry result of thepatches to adjust amount of color materials to suppress the colordeviation. The adjustment of color material is also performed bymeasuring volume of ink droplets ejected from individual printing headsto change an image processing in a similar manner for example.

However, when color deviation is caused in an image represented by blackor gray as achromatic colors, such as monochrome image, it is relativelydifficult to adjust the color deviation. Conventionally, gray ofparticularly low density has been frequently represented by superposingbasic three colors of C, M, and Y at substantially the same amount(e.g., see Japanese Patent Laid Open No. 2000-198227). In this case,even a small change in amounts of color materials of the respectivecolors distorts the balance among the three colors, causing a relativelylarge shift of a hue. This makes it difficult to adjust the amount ofthe color materials itself. Furthermore, even a small change of the sizeof formed dots causes a significant change of the colors due to the samereason. This color deviation in gray means that a color of a chromaticcolor is slightly visible in the achromatic color, and thus the colordeviation is noticeably observed.

FIG. 1 shows the contents of look-up table (LUT) for a color conversiondescribed in Japanese Patent Laid Open No. 2000-198227 for a case wherea gray image is printed. The horizontal axis represents 0 to 255 densitylevels (density values) represented by the respective 8 bit input dataof R, G, and B for example for colors on a gray axis in a color spacewhile the vertical axis represents output signal values (0 to 255) ofthe respective color inks, that is, ink amount (color material amount))in order to express the respective density values. As shown in FIG. 1,gray is expressed by the three color inks of C, M, and Y in a range froma low density region to an intermediate density region. Specifically,output values of the respective three color inks shown in FIG. 1 aredetermined as gray having no color deviation in a predetermined colorspace. When the input density level exceeds about 176, the use of blackink (K) is started and the output signal value at the highest densitylevel is about 128.

FIG. 2 shows another example of a conventional color conversion LUT.FIG. 2 shows, as in FIG. 1, ink amounts of the respective colors toexpress the colors of the gray axis in a color space. The example shownin FIG. 2 shows the color conversion LUT for a case where, in additionto cyan (C) ink and magenta (M) ink, light cyan (lc) and light magenta(lm) ink for which colorant such as dye has a lower density are used.

Recently, a high quality image comparable to an image by the silverhalide photography has been required in the ink jet printer field. Oneof the major problems in this case is granular quality provided by aprinted image to an observer. This granular quality is so-called visualroughness given to an observer when dots formed on a printing medium areconspicuous at a level that can be visually recognized. In order toreduce such granular quality, a plurality of types of inks for similarcolors are used that have colorants having different densities asdescribed above.

As shown in FIG. 2, in a low density region, inks of three colors of lc,lm, and Y are used to express gray. A process where the density isgradually increased from a low density causes discrete formation ofdots. Thus, the inks having a lower density are used to reduce thegranular quality. Output values of the respective three inks in thisexample are also determined as gray having no color deviation in apredetermined color space. In a region of an intermediate density,output values of lm and lc are close to the maximum value and thus thecombination of these inks cannot express a further higher density. Thisdensity region also causes a great number of dots to be closely arrangedon a printing medium, thus suppressing the granular quality due toindividual dots from being conspicuous. Thus, C and M, and further K canbe gradually added when this density region is approached to increasethe density while suppressing the granular quality from appearing. Atthe same time, the output values of lc, lm and Y are graduallydecreased. Finally, the output value of K has a value higher than thoseof the other inks, thus providing an expression of gray or black havinga superior tone.

However, the methods for determining the ink amount described withreference to FIG. 1 and FIG. 2 as described above have the difficulty inadjustment of the color deviation of a monochrome image of gray or blackas described above and also cause conspicuous color deviation.

In addition to these methods, Japanese Patent Laid Open No. 2000-198227describes a mode for printing black characters or the like in which, inorder to express a color of the gray axis, black (K) ink is used inwhole regions from a low density region to a high density region. Whenis the granular quality is not required to be particularly considered,gray or black can be expressed by using K ink in whole density regions.This can suppress the color deviation due to unbalance in a case wheregray is expressed by the three colors of C, M, and Y for example.

However, the above case may cause the color deviation where anunintended color appears in a monochrome image due to a characteristicowned by K ink itself or a relation between the K ink and a printingmedium.

Furthermore, Japanese Patent Laid Open No. 2000-198227 does not suggestthe use of K ink for whole density regions for colors other than thoseof the gray axis. Specifically, such a monochrome image also may berequired that has some color tone, such as cold tone, warm tone, otherthan a pure black tone having a perfectly neutral color tone. Thisallows various monochrome images according to user's preference to beprinted. In this case, it is desirable that a color adjustment isexecuted for the monochrome images so that monochrome images free fromthe color deviation and having adjusted color tone can be printed.However, it is clear that this request cannot be satisfied by only thetechnique as described in Japanese Patent Laid Open No. 2000-198227 forusing K ink in whole density regions for colors of the gray axis.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide an imageprocessing apparatus, a printing apparatus, and an image processingmethod that can suppress the color deviation to print a favorablemonochrome image.

In a first aspect of the present invention, there is provided an imageprocessing apparatus comprising:

color conversion means for converting color signals representative of animage into signals corresponding to color materials used for printingthe image.

wherein the color conversion means converts the color signals into thesignals corresponding to color materials so that the color material ofan achromatic color is used in all of a color gamut including a grayaxis and regions other than the gray axis.

Here, the color conversion may mean converts the color signals into thesignals corresponding to color materials so that the color material of achromatic color is used at an amount smaller than that of the colormaterial of the achromatic color.

In a second aspect of the present invention, there is provided aprinting apparatus for printing an image based on signals correspondingto a color material used for printing the image, the apparatuscomprising:

color conversion means for converting color signals representative of animage into signals corresponding to color materials used for printingthe image,

wherein the color conversion means converts the color signals into thesignals corresponding to color materials so that the color material ofan achromatic color is used in all of a color gamut including a grayaxis and regions other than the gray axis.

In a third aspect of the present invention, there is provided an imageprocessing method comprising:

a color conversion step of converting color signals representative of animage into signals corresponding to color materials used for printingthe image,

wherein the color conversion step converts the color signals into thesignals corresponding to color materials so that the color material ofan achromatic color is used in all of a color gamut including a grayaxis and regions other than the gray axis.

In a fourth aspect of the present invention, there is provided an imageprocessing apparatus comprising:

means capable of setting a plurality of printing modes including amonochrome mode for printing a predetermined monochrome image and acolor mode for printing a color image;

first color conversion means for converting color signals representativeof the monochrome image into signals corresponding to color materialsused for printing the monochrome image, when the monochrome mode is setas the printing mode; and

second color conversion means for converting color signalsrepresentative of the color image into signals corresponding to colormaterials used for printing the color image, when the color mode is setas the printing mode,

wherein the first color conversion means converts the color signals intothe signals corresponding to color materials so that the color materialof an achromatic color is used in all of the color gamut including agray axis and hues other than the gray axis,

wherein the second color conversion means converts the color signalsinto the signals corresponding to color materials so that the colormaterial of an achromatic color is used in a part of the color gamutincluding the gray axis and hues other than the gray axis, and

wherein the color gamut used for color conversion by the first colorconversion means is smaller than that of a color gamut used for thesecond color conversion means.

In a fifth aspect of the present invention, there is provided an imageprocessing apparatus comprising:

color adjustment means for performing a color adjustment for amonochrome image; and

color conversion means for converting color signals representative ofthe monochrome image, which is subjected to the color adjustment by thecolor adjustment means, into signals corresponding to color materialsused for printing the monochrome image,

wherein the color conversion means converts the color signals into thesignals corresponding to color materials so that the color material ofan achromatic color is used in whole density range, which is defined bythe color signals, in a gray axis and respective hues other than thegray axis in a color gamut including the gray axis and the hues.

In a sixth aspect of the present invention, there is provided an imageprocessing apparatus comprising:

means for a monochrome mode for printing a predetermined monochromeimage;

means for discarding a color component of color signals representativeof an image to be printed when the monochrome mode is set;

means for performing a color adjustment for color signals colorcomponent of which has been discarded; and

color conversion means for converting color signals, which is subjectedto the color adjustment, into signals corresponding to color materialsused for printing the monochrome image,

-   -   wherein the color conversion means converts the color signals        into the signals corresponding to color materials so that the        color material of an achromatic color is used in whole density        range, which is defined by the color signals, from a low density        to a high density in a gray axis and respective hues other than        the gray axis in a color gamut including the gray axis and the        hues.

In a seventh aspect of the present invention, there is provided an imageprocessing method comprising:

a color adjustment step of performing a color adjustment for signalsrepresentative of a monochrome image; and

a color conversion step of converting color signals representative ofthe monochrome image, which is subjected to the color adjustment, intosignals corresponding to color materials used for printing themonochrome image, by using a color conversion table,

wherein the color conversion table is a table which converts the colorsignals into the signals corresponding to color materials so that thecolor material of an achromatic color is used in whole density range,which is defined by the color signals, in a gray axis and respectivehues other than the gray axis in a color gamut including the gray axisand the hues.

In a eighth aspect of the present invention, there is provided a programfor causing a computer to execute a color conversion processing forconverting color signals representative of an image into signalscorresponding to color materials used for printing the image,

wherein the color conversion processing converts the color signals intothe signals corresponding to color materials so that the color materialof an achromatic color is used in all of a color gamut including a grayaxis and regions other than the gray axis.

According to the above-described configuration, in every regions of acolor reproduction region which include regions of a gray axis andregions other than those of the gray axis, achromatic color materialsare used in whole density regions defined by image data. Thus, when amonochrome image of a black or a gray color is printed, a low densityregion and so on of the image also can be printed by achromatic colormaterial such as black ink. This can suppress a color deviation due toan imbalance among three chromatic color materials of cyan, magenta andyellow when black or gray color of this low density region is expressedby these chromatic color materials.

Furthermore, the color reproduction region for which whole densityregions use achromatic color material also includes not only regions ofthe gray axis but also regions surrounding these regions. Thus, evenwhen bluish black or bluish gray color for example is desired by a coloradjustment for a monochrome image, an appropriate color conversion isperformed to suppress the color deviation.

Furthermore, according to a preferable aspect of the invention, colormaterial of the chromatic color is used, in whole density regions, at anamount smaller than that of color material of the achromatic color.Thus, a color deviation, in which different colors from the intendedones are printed due to for example the characteristic of color materialitself of an achromatic color and a relative color developingcharacteristic to a printing medium can be suppressed by using the abovechromatic color so that the above chromatic color counterbalances thecolor deviation.

The above process can suppress the color deviation and thus print afavorable monochrome image.

The above and other objects, effects, features and advantages of thepresent invention will become more apparent from the followingdescription of embodiments thereof taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the contents of a color conversion look-up table (LUT) whena conventional gray color image is printed;

FIG. 2 shows another example of a conventional color conversion LUT;

FIG. 3 is a perspective view illustrating the main structure of an inkjet printer according to one embodiment of the present invention;

FIG. 4 is a schematic view illustrating ejection opening faces ofprinting heads of the respective Inks shown in FIG. 3;

FIG. 5 is a block diagram illustrating a printing system of theembodiment structured to include the ink jet printer of the embodimentand a host computer for the printer;

FIG. 6 is a block diagram for explaining an image processing performedby a CPU 102 shown in FIG. 5;

FIG. 7 is a flowchart illustrating an image processing by a hostcomputer 101 and related processing, including a color conversionprocessing for determining an ink amount in the case of a monochromeprinting according to a first embodiment of the present invention;

FIG. 8 is a view showing an example of a display screen of a CRT 108 forselecting a print mode in the processing of FIG. 7;

FIGS. 9A-9G are diagrams schematically showing look-up tables (LUT) usedin the post process of the color conversion processing in a conversionprocessing 2 in processing of FIG. 7;

FIG. 10 is a diagram showing a gamut according to the first embodimentcompared with a gamut in the case of color printing;

FIG. 11 is a view showing a screen of “monochrome photograph color toneadjustment” according to the first embodiment;

FIG. 12 is a flowchart showing an image processing by a host computer101 and related processing, including a color conversion processing fordetermining an ink amount in the case of a monochrome printing accordingto a second embodiment of the present invention;

FIG. 13 is a view showing an example of a display screen of the CRT 108for selecting a printing mode in the processing of FIG. 12;

FIGS. 14A and 14B are diagrams schematically showing a look-up table(LUT) used in the post process of the color conversion processing in theconversion processing 2 in the processing of FIG. 12;

FIG. 15 is a diagram showing a gamut according to the second embodimentcompared with a gamut used in the case of color printing; and

FIG. 16 is a view showing a screen of “manual color tone adjustment”according to the second embodiment.

DETAIL DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings.

First Embodiment

FIG. 3 is a perspective view illustrating the main structure of an inkjet printer according to one embodiment of the present invention. InFIG. 1, a reference numeral 1 denotes a printing medium such as a paper,a plastic sheet. Before printing is started, the printing media 1 arelayered in a cassette (not shown) or the like. When printing is started,the printing media 1 are fed one by one into a printer apparatus by apaper-feed roller (not shown). A reference numeral 3 denotes a firstpair of transport rollers and a reference numeral 4 denotes a secondpair of transport rollers, respectively. These pairs of rollers arearranged in a substantially vertical direction with a predeterminedinterval therebetween. The first pair of transport rollers 3 and thesecond pair of transport rollers 4 are rotated by driving force of therespective stepping motors (not shown) to intermittently transport, by apredetermined amount, the printing medium 1 sandwiched by these pairs ofrollers in the direction of an arrow A.

Reference numerals 5 a to 5 f denote Ink tanks for storing ink suppliedto respective corresponding printing heads 11. The ink tank 5 a storesyellow ink (Y), the ink tank 5 b stores magenta (M) ink, the ink tank 5c stores cyan (C) ink, the ink tank 5 d stores light magenta (lm) ink,the ink tank 5 e stores light cyan (lc) ink, and the ink tank 5 f storesblack (K) ink, respectively. Front sides of the respective ink tanks(printing medium side) are connected with the corresponding printinghead 11 via an ink supply path. In this manner, an ejection opening facein which ink ejection openings of the printing head 11 are provided isopposed to the printing medium 1 sandwiched by the first pair oftransport rollers 3 and the second pair of transport rollers 4 to have agiven tension. It is noted that the printing heads 11 for ejecting theabove six colors of ink may be independently provided for the respectivecolors or may be provided integrally.

The printing heads 11 and the ink tanks 5 a to 5 f are mounted in acarriage 6 in a detachable manner. A reference numeral 10 denotes acarriage motor that transmits the driving force thereof via two pulleys8 a and 8 and a belt 7 to the carriage 6, thereby reciprocating thecarriage 6 in the direction shown by an arrow B. Then, the scanningdirection of the carriage 6 is guided and supported by a guide shaft 9.

A reference numeral 2 denotes a recovery unit for performing amaintenance processing of the printing head 11. The printing heads 11are moved, as required, to a home position at which the recovery unit 2is provided to use the recovery unit 2 to perform the recoveryprocessing such as a preliminary ejection, suction recovery, wiping orthe like.

When printing is performed, the carriage 6 is moved in the directionshown by an arrow B during which the respective printing heads 11 ejectink droplets depending on a printing signal with an appropriate timing.When this one printing scan by the printing heads 11 is completed, thepair of transport rollers 3 and 4 transport the printing medium 1 by apredetermined amount. By repeating the printing scanning and thetransport of the printing medium as described above, an image is formedon the printing medium 1 sequentially.

FIG. 4 is a schematic view illustrating ejection opening faces ofprinting heads 11K, 111 c, 111 m, 11C, 11M, and 11Y of the respectiveinks. (the ejection opening rows of) the respective printing heads arearranged at the same position as that of the ink tank 5, as shown inFIG. 4, in the direction shown by the arrow B along which the printingscan is performed. In an ejection opening row of each ink, 512 ejectionopenings are arranged in the direction shown by the arrow A along whicha printing medium is transported and with a pitch of about 40 μm. Thisallows, when the respective printing heads 11 provide one printing scan,the printing medium 1 to have thereon an image having a resolution of600 dpi (dot/inch: reference value).

In this embodiment, an ejection opening of each printing head ejects anink droplet of about 2 ng (2 Pl). In the printer of this embodiment,this ink amount of 2 ng is “an amount at which black ink applied on aprinting medium in a discrete manner causes a granular quality butcauses almost no problem in a general distance of distinct vision”. Itis noted that the present invention is not limitedly applied to the useof a minute ink droplet as described above. For example, it is clearthat the present invention can be effectively applied regardless of anamount of ink droplets when suppression of color deviation is mainlyrequired e.g., when a printed image having granular quality causes asmall problem or when a user desires the suppression of color deviationand is not concerned about granular quality.

FIG. 5 is a block diagram showing a printing system of this embodimentstructured to include the ink jet printer of this embodiment asdescribed above and a host computer for the printer.

A host computer 101 includes: a CPU 102, a memory 103, a second memory104, an input section 105, a CRT 108, and an interface 106 for example.

The CPU 102 executes a program stored in the second memory 104 toperform an image processing which will be described later with referenceto FIG. 6, FIG. 7 and FIG. 12 and overall processing involved withprinting. The memory 103 is used as a work area for performing an imageprocessing and as a temporary storage region for image data. A programfor executing a processing for converting image data also may besupplied from an external apparatus (not shown) for example to the hostcomputer 101. While confirming the CRT 108, a user uses the inputsection 105 to input various commands.

The host computer 101 is connected with an ink jet printer 107 via theinterface 106. The CPU 102 sends print data processed through the imageprocessing to the ink jet printer 107 to cause the ink jet printer 107to perform printing operation.

FIG. 6 is a block diagram for explaining an image processing performedby the CPU 102 shown in FIG. 5. In this embodiment, brightness signalsof red (R), green (G), and blue (B) are used as color signalsrepresentative of an image. 8 bit (256 tones) image data represented bythese brightness signals is finally converted to printing data of therespective 1 bit cyan (C), magenta (M), yellow (Y), light cyan (lc),light magenta (lm), and black (K) used in the ink jet printer. It isnoted that the entire image processing corresponds to conversionprocessing by step S705 and step S709 which will be described later withreference to FIG. 7, or conversion processing by step S1205 and stepS1210 which will be described later with reference to FIG. 12.

As shown in FIG. 6, the respective 8 bit brightness signals R, G, and Bas color signals representative of an image are inputted to a colorconversion processing section 201. Then these brightness signals R, G,and B are converted to 8 bit density signals of C, M, Y, lc, lm, and K.Here, the conversion is performed by using a three-dimensional colorconversion look-up table (LUT) and an interpolation processing.Specifically, the CPU 102 refers to the LUT to calculate density valuesof the respective C, M, Y, lc, lm, and K corresponding to a combinationof the inputted R, G, and B signal values. Here, the LUT stores onlydensity values to specific discrete R, G, and B data. Thus, theinterpolation processing is performed by using the combinations of aplurality of density values, which are stored to correspond tocombinations of R, G, and B expressed by 256 levels for each color, tocalculate the combinations of density values corresponding to thecombinations of input R, G, and B values. It is noted that theinterpolation processing performed here is a known technique and thuswill not be described further. A density signal value obtained by thecolor conversion processing 201 is represented by 8 bit as in the caseof an input value and is outputted as image data having tone values(density values) of 256 levels.

Next, the image data that has been subjected to the color conversionprocessing 201 is subjected to the conversion processing by the outputgamma (γ) correction 202. The output gamma correction section 202corrects the data for each ink color so that the optical density finallyexpressed on a printing medium can have linearity to an inputted densitysignal. Here, the gamma correction is performed by referring toone-dimensional look-up tables independently prepared for the respectivecolors. The output signal from the output gamma correction 202 is 8 bitdensity value data as in the case of the input value.

Next, the 8 bit density value data outputted from the output gammacorrection 202 is subjected to a quantization processing 203. In the inkjet printer of this embodiment, each of ink droplets ejected from theprinting head is 2 ng. Thus, the densities of the respective pixels on aprinting medium are represented at two levels that are determinedaccording to whether a 2 ng ink droplet is applied or not. In an areahaving a size which is formed by a group of a plurality of pixels, thedensity is shown in a macroscopic manner by the number of pixels inwhich ink dots are formed. The method for representing the density asdescribed above is generally called as an area coverage modulationmethod. A printing apparatus using the area coverage modulation methodrequires a quantization processing for converting multiple value data tobinary data as in this embodiment. The quantization processing may beperformed by several methods and can be performed by known errordiffusion method or dither method. The binary image data represented by1 bit for each color quantized by the quantization processing 203 istransferred to the ink jet printer and a printing operation isperformed.

An optimal conversion method in the color conversion processing 201, theoutput gamma correction 202, and the quantization processing 203 asdescribed above is generally different depending on the type of aprinting medium or the type of an image to be printed for example. Inparticular, look-up tables used by the color conversion processing 201and the output gamma correction 202 are generally prepared for therespective types of printing media.

FIG. 7 is a flowchart showing an image processing by the host computer101 and related processing, including a color conversion processing fordetermining an ink amount in the case of the monochrome printingaccording to a first embodiment of the present invention.

This processing is started when a user instructs a printing operationvia an application. First, the CPU 102 causes the CRT 108 to display ascreen through which a print mode is selected (step S701).

FIG. 8 shows an example of this display screen. The ink jet printer ofthis embodiment can provide printing for a plurality of types ofprinting media and has appropriate printing modes depending on therespective printing media. This setting or selection of the printingmode is performed by allowing a user to input several conditions via thescreen shown in FIG. 8. In this embodiment, an auto pallet 81 is used toset the type of an image to be printed (e.g., document or photograph).Furthermore, a paper type 82 is used to set the type of a printingmedium to be printed. Furthermore, a monochrome mode for printing adesired monochrome image can be set by checking a checkbox in a grayscale printing 83.

Referring to FIG. 7 again, the subsequent step S702 determines whetherthe set printing mode is a monochrome photograph mode or not. In thisembodiment, this “monochrome photograph mode” is set when the checkbox83 is used to select the gray scale printing and when the paper type 82is used to select a professional photo paper. When the checkbox 83 isused to select a gray scale printing and the paper type 82 is used toselect the types other than the professional photo paper, then a normalmonochrome mode (gray scale printing) other than “monochrome photographmode” is set.

When step S702 determines that the set print mode is the monochromephotograph mode, the processing proceeds to step S706. Step S706performs a processing for discarding color components of color signalsrepresenting the monochrome image, specifically color informationrepresented by R. G, and B. More specifically, R, G, and B signals ofthe image data, which are signals representing the image, are convertedto brightness signals of gray tone (R=G=B). This conversion is performedby using, when assuming that a brightness signal value of an achromaticcolor to be found is L, a conversion expression of L=0.3 R+0.6 G+0.1 Bto substitute R, G, and B and replacing signals R, G, and B by L. Thisprocessing provides the discard of color information (color component)considering a certain level of luminance. After discarding of the colorcomponents at step S706, the processing proceeds step S707.

Step S707 determines, for a monochrome photograph image, whether coloradjustment for providing a cold tone or a warm tone is performed or not.This is determined by confirming whether the checkbox in a settingscreen of “monochrome photograph color tone adjustment” shown in FIG. 11is checked or not.

When it is determined that the color tone adjustment processing is to beperformed, then step S708 adjusts the color tone in accordance with aslide amount of a slider shown in FIG. 11. Specifically, in the case ofa warm tone, the value L obtained in step S706 is used to adjust thecolor tone based on a formula (1) as shown below.R=INT(255×(L/255)^(1/(1−m)))G=INT(255×(L/255)^(1/(1+m)))B=INT(255×(L/255)^((1+m)))  (1)

In the above formula, “m” denotes a tone adjustment coefficientcorresponding to the slide amount of the above slider operated by auser, and is adjusted, for example, within a range of 0<m<0.5. As aresult, the image data is adjusted to be data showing a relation thatthe respective values of R and G are greater than the value of B. Thatis, data of R, G and B that has been adjusted to be the warm tone has arelation R=G>B.

In the case of the cold tone on the other hand, the color tone isadjusted based on a formula (2) as shown below.R=INT(255×(L/255)^((1−m)))G=INT(255×(L/255)^((1−m)))B=INT(255×(L/255)^(1/(1−m)))  (2)

In the above formula, “m” denotes the tone adjustment coefficientcorresponding to the slide amount as described above and is adjusted,for example, within a range of −0.5<m<0. As a result, the image data isadjusted to be data having a relation that the value of B is greaterthan the respective values of R and G. That is, data of R, G and B thathas been adjusted to be the cold tone has a relation B>R=G.

Addition

By the way, the above-described adjustment for a warm tone and a coldtone may be performed by a one-dimensional look-up table (LUT). Forexample, one-dimensional LUTs are prepared for respective setting levelsfor a warm tone or a cold tone and a LUT corresponding to the set levelis used to execute conversion of R, G, and B signal values. In thiscase, however, one-dimensional LUTs are required to be prepared to thenumber obtained by summing up warm tone setting levels and cold tonesetting levels, causing a system for the color adjustment to be largescale and complicated. This also requires, when a sepia tone, a violettone, or a cyan tone for example is required for a special applicationother than those for a warm tone and a cold tone, anotherone-dimensional LUT to be prepared for the application.

On the contrary, according to the embodiment of the present invention,the R, G, and B signals obtained by the adjustment for the warm tone andthe cold tone as described above are converted to color material amountsignals by using a single three-dimensional LUT that assumes the R, Gand B signals as an input, which will be described later with referenceto FIGS. 9A-9G and FIG. 10. This eliminates the above conventional needfor preparing LUTs to the number of setting levels. In other words,according to the embodiment of the present invention, the coloradjustments for the warm tone and the cold tone are performed as in thesame manner as that in general color conversion as a color adjustment.Accordingly, even in the case of a sepia tone and so on for a specialapplication, color adjustments for these special tones can be performedby using a single LUT, as long as executing a processing for obtainingcorresponding R, G, and B signals to the special tones. Then, the singleLUT can effectively decrease the color deviation for the coloradjustment.

Referring to FIG. 7 again, subsequent to this color adjustment of stepS708 is performed, then the processing proceeds to step S709. If step S707 determines not to perform the color adjustment, the processingdirectly proceeds to step S709. Step S709 executes conversion processing2 unique to the monochrome photograph mode. Specifically, when the coloradjustment processing of Step S708 is performed, the color signals (R,G, and B signals) adjusted based on the above two formulae are convertedthorough conversion processing 2 to signals corresponding to colormaterials (C, M, Y, K, lc, lm). On the other hand, when the coloradjustment processing of Step S708 is not performed, the color signalshaving the value of L (that is L=R=G=B) obtained at step S706 areconverted thorough conversion processing 2 to signals of color materials(C, M, Y, K, lc, lm).

The conversion processing 2 includes the color conversion processing 201described as referring to FIG. 6. The color conversion processing 201uses a three dimensional look-up table exclusive for a monochromephotograph mode to determine uses of inks, which will be described laterwith reference to FIG. 9A-9G. As a result, a monochrome photograph-toneimage free from color deviation can be printed. Specifically, this colorconversion processing generates signals corresponding to use amounts ofblack ink and other colors of inks so that the black ink is used in agreater amount than those of the other colors of inks in whole densityregions (whole density ranges) ranging from a low density region to ahigh density region, in every regions of a color reproduction region(color gamut) according to this color conversion processing or in everyhues as well as the entire achromatic axis (gray axis).

It is noted that the conversion processing 2 includes a series of imageprocessing steps (color conversion processing 201, output gammacorrection 202, quantization 203) described with reference to FIG. 6 asdescribed above. Accordingly, the processing of step S709 convertsdensity signals of 8 bit obtained by the color conversion processing 201to binary print data of 1 bit through the output gamma correction 202and the quantization process 203.

Referring to FIG. 7 again, when Step S702 determines that the mode isnot the monochrome photograph mode, the processing proceeds to step S703to determine whether a monochrome mode other than “monochrome photographmode” is set or not. Specifically, as described for step S702, whetherthe checkbox 83 of “gray scale printing” in the user interface screenshown in FIG. 8 is checked or not is determined. When it is detectedthat the checkbox 83 is checked, the processing proceeds to step S704 toconvert, as in the processing of step S706, the R, G, and B imagesignals to brightness signals of gray tone (R=G=B). Then, the processingproceeds to step S705. When it is determined that the checkbox 83 of thegray scale printing is not checked on the other hand and is thusdetermined that a color mode is set, the processing directly proceeds tostep S705.

Step S705 performs a conversion processing 1 for the image data. Theconversion processing 1 also includes, as in the conversion processing2, the series of image processing steps (201, 202, 203) described forFIG. 6. However, the conversion processing 1 has a color conversionprocessing 201 different from that of the conversion processing 2.Specifically, when the processing directly goes to step S705 withoutgoing through step S704, then the conversion processing 1 uses a knowncolor conversion processing table for a color mode to generate densityvalue signals corresponding to the respective colors of inks requiredfor printing a color image. It is noted that in the color conversionprocessing table for the color mode, black ink is not used in every huesof a color reproduction region (color gamut) including a gray axis andhues other than the gray axis but is only used in a part of the colorreproduction region (specifically in the gray axis and neighborhoodthereof). Also, when the processing reaches step S705 via step S704, theconversion processing 1 similarly uses the above-described colorconversion processing table for the color mode. However, since the colordata (color component) has been discarded, density value signalscorresponding to the respective colors of inks required to print a grayscale image are generated. This generation process includes the colorconversion of gray axis as shown in FIG. 2. Further in step S705,respective 8 bit of density signals corresponding to respective colorsof ink obtained by the color conversion processing 201 are converted tobinary print data represented by 1 bit for each of colors, through anoutput gamma correction processing 202 and a quantization processing203.

The image data subjected to the conversion processing of step S705 orstep S709 is sent to the ink jet printer 107 (Step S710). The ink jetprinter performs a printing operation to a printing medium based on thussent binary print data.

In this embodiment, the monochrome photograph mode is set only when aprinting medium is a professional photo paper. Thus, the conversionprocessing 2 provided in the step S709 uses a processing methodexclusive for the professional photo paper. When it is determined thatthe mode is not a monochrome photograph mode, the conversion processing1 provided in the Step S705 can handle a plurality of types of printingmedia. Specifically, different look-up tables are prepared for varioustypes of printing media regarding the color conversion processing andthe output gamma correction. Thus, the conversion processing 1 providesconversion suitable for each type of printing medium. The processinghere has been described, in order to make comparison between themonochrome photograph mode and those other than the monochromephotograph mode, as the one branching to two processing's as shown inFIG. 7.

FIGS. 9A-9G schematically illustrate a look-up table (LUT) used in thecolor conversion processing 201 in the conversion processing 2. FIGS. 9Ato 9G show a gray axis line table, a cyan line table, a magenta linetable, a yellow line table, a red line table, a green line table, and ablue line table, respectively. In each figure, a horizontal axis denoteslattice points on each line of the LUT. These lattice points are definedby the R, G and B signal values described above. A vertical axis denotesdensity values of C, M, Y, K, lc and lm corresponding to the latticepoints. That is, the vertical axis denotes respective ink amounts usedto express the color of (the lattice point of) of the lines. The grayaxis line of the table shown in FIG. 9A is a line in the LUT forconnecting a lattice point of white with a lattice point of black. Thecyan line of the table shown in FIG. 9B is a line passing through theabove white lattice point via cyan lattice point to the black latticepoint and passes a lattice point of the maximum chroma of cyan hue inthe color reproduction region (color gamut). The lines of the tablesshown in FIG. 9C to 9G are also those similar to the cyan line thatpasses the maximum chroma points of the respective hues. It is notedthat ink amount (of the lattice points) on the shown lines is obtained,for example, by the colorimetry result of a printed patch and ink amountof a lattice point on a line other than these lines is determined by aninterpolation processing.

The lines on the LUT of this embodiment, which are the tables shown inFIG. 9A-9G, are lines that are in a color reproduction region (colorgamut) smaller than a color reproduction region in the case of theconversion processing 1 as shown in FIG. 10, and are significantlydifferent from the table of the conversion processing 1 with regards tothe way to use inks. Specifically, even when the color tone adjustmentof step S708 is performed in the monochrome photograph mode, themonochrome image is an image of basically gray or black and a colorreproduction region is a small gamut in which a periphery of the grayaxis has not so much large (high) chroma. FIG. 10 is a diagram showing agamut 1001 of this embodiment seen from the above part of the luminance(L*) axis that is compared with a gamut 1002 in the case of colorprinting. As shown in FIG. 10, the gamut 1001 has a relatively smallchroma value (a*, b*) compared to that of the gamut 1002.

As a first feature, the LUT of this embodiment shown in FIGS. 9A to 9Guses black ink in whole density ranges from a low density to a highdensity in each of a gray axis and respective hues, which are in a colorreproduction region (gamut 1001 show in FIG. 10) including the gray axis(FIG. 9A) and regions (FIGS. 9B to 9G) other than the gray axis. Theblack ink maintains, in whole density ranges, higher output values thanthose of other color inks. This black ink amount increasesmonotonically. By using black ink in whole density regions defined byimage data in order to print a monochrome image as described above, theuse of C, M, and Y to express a monochrome image can be avoided, thusdecreasing the color deviation due to slight imbalance in ink amountamong these three colors. In other words, a chromatic color ink is usedtogether with black ink even in a low density region. In this case,these chromatic color inks do not have a role to reduce granular qualityor a role as basic colors to form gray while having balance there among.Thus, even when a density value changes, the output value of thechromatic color only increases monotonically. Thus, they are preventedfrom crossing one another and concern that the color deviation may becaused as the conventional monochrome mode described with reference toFIGS. 1 and 2 is almost eliminated. It is noted that, although black inkhere exemplarily has a curve at which the brightness γ≈1.8, the value ofthe brightness γ is not limited to this.

As a second feature, the LUT of this embodiment uses at least onechromatic color ink in addition to black ink in the respective regions.FIG. 9A-9G shows examples that two chromatic color inks of cyan andyellow or two chromatic color inks of magenta and yellow are used. It isnoted that in a narrow part of the darkest part, three colors are used.These chromatic colors maintain the output values thereof at low levels.Specifically, a chromatic color used in this embodiment is used toexpress the hue of the region, e.g. the hue of cyan of the cyan lineshown in FIG. 9B and is used to suppress the color deviation due to thecharacteristic of black ink itself used in that region or a relativecharacteristic of black ink with a printing medium. For example, if thecharacteristic of black ink or the relative characteristic is bluishgray or bluish black, then a chromatic color for counterbalancing thisto prevent the bluish color from coming out is used. This also appliesto the gray axis shown in FIG. 9A. In the examples shown in FIGS. 9A to9G, at least one type of chromatic color ink (yellow ink, cyan ink ormagenta ink in this example) among two types of chromatic color inks(cyan ink and yellow ink or magenta ink and yellow ink depending on aregion) is used, as with black ink, in whole density regions from a lowdensity region to a high density region, and other chromatic color Ink(cyan ink or yellow ink depending on a region) is used starting from theintermediate density region. By using at least one type of chromaticcolor ink together with black ink, the color deviation due to thecharacteristic of black ink can be suppressed when a monochromephotograph image is printed.

Compared to this, the conventional color conversion tables shown in FIG.1 and FIG. 2 shows the increase or decrease of signal values that is notmonotonic and cause the respective colors to cross one another at somepoints. This kind of condition causes a situation where the colordeviation tends to be caused. When a printing head having a smallejection amount of ink is used as in this embodiment in particular, thecolor deviation appears more conspicuously, which is an adverse imageeffect for a case where a stable monotone image is required as themonochrome photograph mode.

The use of black ink from a low density region may deteriorate thegranular quality. However, when an amount of discharged ink per one dotis sufficiently small and very few dots are visually found with adistance of distinct vision as in this embodiment, “color deviation”rather than granular quality is an adverse image effect, as describedabove. The present inventors focused attention on the fact that, when aphotograph image having a high quality is desired to be realized, thelevel of an adverse image effect such as “granular quality” and “colordeviation” changes depending on an amount of to-be-used ink droplets.The present inventors determined that, if the size of dots on a printingmedium is sufficiently small to cause no problem, the suppression of“color deviation” is more important than the suppression of granularquality. Furthermore, the above concept is applied to parts other thanthe gray axis in a gamut. This can suppress “color deviation” even whena color tone adjustment function is included, thus providing amonochrome photograph having high quality.

The size or conspicuousness level of dots formed on a printing mediumchange depending on the color or characteristic of the printing medium.Thus, “what amount of discharged ink can prevent granular quality frombeing conspicuous” does not have a single clear answer. However, judgingfrom generally-provided ink jet printers and printing media adaptable tothe printers, an amount of ink of 5 ng or less per one dot causes almostno problem and the amount is more preferably 2 ng or less.

Modified Example

The above example has described an example where, only when an image tobe printed is assumed to be a photograph image, i.e. only when a grayscale printing is selected and a professional photo paper is selected asa printing medium, the conversion processing 2 according to oneembodiment of the present invention is performed. However, thisembodiment is not limited to this example. For example, anotherconfiguration may be used where, even when an image to be printed is nota photograph image, the conversion processing 2 is performed if the grayscale printing is selected. That is, a configuration may be used inwhich, regardless of whether an image to be printed is a photographimage or not, the conversion processing 2 is performed when themonochrome mode for outputting the image by the gray scale is selected.This configuration can suppress color deviation not only when an imageto be outputted is a monochrome photograph image but also in the entiregray scale image.

Addition Second Embodiment

A second embodiment of the present invention is almost the same as thefirst embodiment as described above but is significantly different fromthe first embodiment in an operation by a user for the color adjustmentin a monochrome photograph mode and a configuration for obtaining anadjusted value depending on the color adjustment. Hereinafter, thesedifferences between the second embodiment and the first embodiment willbe mainly described. It is noted that the second embodiment is based onthe same printing system as those shown in FIG. 3 to FIG. 6.

FIG. 12 is a flowchart showing image processing and related processingby the host computer 101, including a color conversion processing fordetermining an ink amount in the case of a monochrome printing accordingto the second embodiment of the present invention.

This processing is started when a user instructs a printing operationvia an application. Then, the CPU 102 firstly displays, on the CRT 108,a screen through which a printing mode is selected (Step S1201).

FIG. 13 is a view showing an example of this display screen. An ink jetprinter of this embodiment can provide printing on a plurality of typesof printing media and have appropriate printing modes in accordance withthe respective printing media. This setting or selection of a printingmode is performed by allowing a user to input several conditions via thescreen shown in FIG. 13. In this embodiment, a text box 1301 can beused, as shown in FIG. 13, to set which type of printing medium isprinted. A radio button 1302 is used to set whether the adjustment ofcolor and density is performed automatically or manually. A checkbox1303 is used to set a monochrome printing.

With reference to FIG. 12 again, the subsequent step S1202 determineswhether the set printing mode is a monochrome photograph mode or not. Inthis embodiment, this “monochrome photograph mode” is set when themonochrome printing is selected via the checkbox 1303 and when aprofessional photo paper is selected via the text box 1301. When themonochrome printing is selected via the checkbox 1303 and a paper typedifferent from the professional photo paper is selected via the text box1301, then the normal monochrome mode (gray scale printing) other than“monochrome photograph mode” is set.

When step S1202 determines that the printing mode is the monochromephotograph mode, “discard of color data” is performed as in the firstembodiment (step S1207). However, in this embodiment, prior to the“discard of color data”, step S1206 inputs a coefficient used for thediscard of color data. As described above in the first embodiment, thediscard of color data converts R, G, and B signals to a brightnesssignal L. Thus, a coefficient of the conversion equation (channel mixingcoefficient) is inputted. Coefficients of 0.3, 0.6, and 0.1 of therespective R. G, and B in this conversion equation are thegenerally-used ones. A user can input these coefficients via a userinterface (not shown) as an operation of a color filter to provide amonochrome mode (discard of color data).

After the above step, step S1207 performs a processing for discardingcolor information (color component) represented by R, G, and B. Thisprocessing is the same as that of the first embodiment but is differentfrom that of the first embodiment in that coefficients a, β, and γ in aconversion equation L=aR+BG+γB are values inputted by step S1206 asdescribed above.

Next, step S1208 determines whether a color adjustment for a cold toneor a warm tone is performed or not with regards to the monochromephotograph image. This is judged based on the position of the slider foradjusting “monochrome color tone” shown in FIG. 16. Specifically, whenthe slider for “monochrome color tone” is slid from a neutral positionto a warm tone or a cold tone, color adjustment for a warm tone or acold tone is judged to be performed. Step S1208 determines that thecolor adjustment is performed, the processing proceeds to step S1209. Onthe other hand, Step S1208 determines that the color adjustment is notperformed, the processing directly proceeds to step S1210.

Next, the color adjustment performed in step S1209 will be described.The color adjustment in this step is performed for the R, G, and Bsignals that are obtained as a result of an adjustment of “monochromecolor tone”, “density”, and “contrast” that are the three adjustmentfactors shown in FIG. 16.

FIG. 16 shows a user interface for “manual color adjustment” accordingto the second embodiment. This operation screen is displayed when, inthe user setting (FIG. 13) in step S1201 as described above, themonochrome photograph mode is selected (the monochrome printing 1303 andthe professional photo paper 1301 are selected) and the radio button1302 is used to select the manual adjustment. Specifically, when themonochrome photograph mode is selected, adjustment of “monochrome colortone 1601”, “density 1602”, and “contrast 1603” are active. This allowsa user to operate the respective sliders to adjust the respectivefactors. For example, in “monochrome color tone 1601”, the slider ismoved toward “cold tone” when a cold tone is desired. When this movementis performed, it is judged in step S1208 that the color adjustmentprocessing as described above is performed. In “density 1602”, theslider is moved toward “increase” when increasing the density isdesired. Further, in “contrast 1603”, the slider is moved toward“increase” when the contrast is desired to be increased.

In the operation screen shown in FIG. 16, the above three adjustmentfactors may be used for a multiple adjustment. When a user operates allsliders of the “monochrome color tone 1601”, “density 1602”, and“contrast 1603”, this embodiment changes, depending on the respectiveslide amounts, R, G, and B values in an order of “contrast”, “density”,and “monochrome color tone”. When the sliders of two adjustment factorsamong the three factors are slid, R, G, and B values are changed in anorder observing the order of that two factors in the above order. It isnoted that a user does not always operate the sliders in this order.When a user slides the sliders in an arbitrary order, the respectiveslide amounts are retained. When the above setting is fixed by an “OK”button (FIG. 16), R, G, and B values are converted in the above order.

Firstly, R, G, and B values are changed by the contrast adjustment inthe manner as described below. When it is assumed that the adjustmentvalue (T) for contrast is adjusted by the slider within a range from −50to 50, the respective R, G, and B signals are converted by the followingexpression (3-1) or expression (3-2).

Expression (3-1):

When R, G and B≦128:R′=((R/128)^d)×128G′=((G/128)^d)×128B′=((B/128)^d)×128

where when 0≦T≦50, d=1.00+(0.02×T),

when −50≦T<0, d=1.00/(1.00−(0.02×T))

where 0≦R′, G′, and B′≦255 and “d” is effective to three places ofdecimals.

Expression (3-2):

When 128<R, G, and B:R′=((255−R)/127)^d)×(255−127)G′=((255−G)/127)^d)×(255−127)B′=((255−B)/127)^d)×(255−127)

where when 0≦T≦50, d=1.00+(0.02×T), and

when 50≦T<0, d=1.00/(1.00−(0.02×T).)

Secondly, the R, G, and B values are changed by the density adjustmentas described below. When it is assumed that the adjustment value (T) fordensity is adjusted by the slider within a range from −50 to 50, therespective R, G, and B signals are converted be the following expression(4-1) or expression (4-2).

Expression (4-1)

When −25≦T≦50:R″=((R′/255)^b)×255G″=((G′/255)^b)×255B″=((B′/255)^b)×255

Where when 0≦T≦50, b=1.00+(0.02×T), and

When −25≦T<0, b=1.00/(1.00−(0.02×T)).

It is noted that 0≦R″, G″, and B″≦255, and “b” is effective to threeplaces of decimals.

Expression (4-2)

When −50≦T<−25,R″=((255+c)/255)×(((R′/255)^b)×255)−cG″=((255+c)/255)×(((G′/255)^b)×255)−cB″=((255+c)/255)×(((B′/255)^b)×255)−c

Where b=1.00/1.50, c=(64/25)×(T+25)

Thirdly, in accordance with the slide amount of the slider for themonochrome color tone, R″, G″, and B″ are respectively subjected to thewarm tone expression (1) or the cold tone expression (2) as describedabove for the first embodiment so that R, G, and B values are changed.

As described above, step S1209 integrally resolves, into the R, G, and Bvalues, the respective adjustment values of “monochrome color tone”,“density” and “contrast”. Then, these R, G, and B values are subjected,in the next step S1210, to the “conversion processing 2” similar to stepS709 of FIG. 7 of the first embodiment. This can print, even when amonochrome image is subjected to various adjustments, a high-qualityimage free from color deviation.

This conversion processing 2 is basically the same as the conversionprocessing 2 in the first embodiment. FIGS. 14A and 14B are diagramsschematically showing a look-up table (LUT) used in the color conversionprocessing in the conversion processing 2 of this embodiment and showtables of a gray axis line and a yellow line of LUT as an example. InFIGS. 14A and 14B, the tables are different from the table shown in FIG.9A-9G according to the first embodiment in that both tables of the grayaxis line (FIG. 14A) and the yellow line (FIG. 14B) use light magenta(lm) while the tables shown in FIGS. 9A and 9D use magenta (M). For theother points, the LUT is the same as that of the first embodiment for adensity range in which K is used and the relation between this K and inkamount of other chromatic colors.

Specifically, firstly, the LUT of this embodiment also uses black ink,as in the first embodiment, in whole density ranges from a low densityto a high density of respective regions of a color reproduction regionincluding the gray axis (FIG. 14A) and regions (FIG. 14B) other than thegray axis. Then, the black ink maintains an output value higher thanthose of other color inks in whole density ranges. This black ink amountalso increases monotonically. By using, in order to print a monochromeimage, black ink in whole density regions (whole density ranges) definedby the image data as described above, the use of C, M, and Y for theexpression of a monochrome image is avoided. As a result, colordeviation due to slight imbalance in the ink amount among these threecolor inks can be prevented.

Secondly, in the respective regions of the color reproduction region,two chromatic color inks such as light magenta and yellow are used inaddition to black ink. These chromatic colors maintain the output valuesat low levels. Specifically, two chromatic colors or yellow which is oneof the colors used in this embodiment is used to express a hue in thecolor reproduction region, e.g. yellow hue in the yellow line shown inFIG. 14B and is used to suppress the color deviation due to thecharacteristic of black ink itself used in the color reproduction regionor a relative characteristic of the black ink with a printing medium.

As described above, a maximum chroma point of yellow in a normal colorseparation table defines only an yellow component and does not use othercolor materials. On the other hand, a table having small gamut for amonochrome image such as table used in the conversion processing 2previously determines main color such as warm tone or cold tone. Thus,the maximum chroma point of yellow can be previously adjusted withanother color (lm) to avoid color deviation.

FIG. 15 is a diagram showing a color reproduction region (gamut)according to the LUT used in the conversion processing 1 and a gamut bythe LUT used in the conversion processing 2. FIG. 15 shows therespective gamut represented in an L*a*b* color space observed from thedirection of the L* axis with a bird eye view.

In FIG. 15, a gamut 2001 is a gamut of the LUT used in the conversionprocessing 2 and a gamut 2002 is a gamut of LUT used in the conversionprocessing 1. In FIG. 15, six hue lines are shown for each gamut.Specifically, in the gamut 2001, hue lines 2001Y, 2001R, 2001M, 2001B,2001C, and 2001G of yellow, red, magenta, blue, cyan, and green areshown, respectively. FIG. 14B shows a table of the hue line 2001Y. As inthe first embodiment, the LUT used in the conversion processing 2 usesblack ink in all other hue lines including the hue line 2001Y as well asthe hue lines 2001R, 2001M, 2001B, 2001C, that is, every regions of thecolor reproduction region, and in the whole density regions from a lowdensity region color to a high density region. Then, this gamut 2001 isa color reproduction region smaller than the gamut 2002. Specifically,in the monochrome photograph mode, even when the color tone adjustmentof step S1209 is performed, basically a gray or black monochrome imageis printed and a color reproduction region is of a small gamut havingnot so much (high) chroma around the gray axis.

Third Embodiment

Although the above-described the first and the second embodiments haveparticularly described that black ink is mainly used for hues other thanthe gray axis, a system that can include both of gray ink and black inkor all of the three of light gray ink, dark gray ink and black ink alsocan mainly use such achromatic inks. In this case, density signalspreferably tend to increase in a monotonic manner if possible. Then,chromatic color ink only has a role of suppressing “color deviation” anda density value of the chromatic color ink is set to be smaller than thedensity signal values of the achromatic inks.

Other Embodiments

Although the above embodiments has described the present invention by anexample of the ink jet printing system having the structure shown inFIG. 5, the present invention is not limited to be applied to thisstructure. Respective structures actualizing functions shown in FIG. 5also may be provided in any one of a host computer and an ink jetprinter or may be all integrated to be an image formation system.

Further, although the above embodiments has described a case where aseries of image processing described with reference to FIG. 6 are allperformed by the CPU 102 of the host computer 101, these processing alsomay be partially or entirely performed by the ink jet printer 107 forexample. For example, the color conversion processing 201 and the outputgamma correction 202 may be performed in the host computer 101 andquantization processing 203 may be performed in the ink jet printer 107.Further, the input or setting of the print mode described for FIG. 7also may be not performed by the host computer 107 but performed by theink jet printer.

Furthermore, the screen for setting a print mode described withreference to FIG. 8 or FIG. 13 is also not limited to have theabove-described contents. For example, although the screen of FIG. 8prepares the checkbox 83 for setting a gray scale printing, anotherconfiguration also may be provided, for example, in which a user himselfor herself can set the hue and chroma of an output image via the screenso that it can be determined that the monochrome mode is set when thepredetermined hue and chroma are set.

Although the above embodiments have described the ink jet printingapparatus that can eject six colors of inks, the present invention alsocan be used for printing apparatuses other than an ink jet printingapparatus so long as the printing apparatuses can use a plurality ofcolor materials to represent a color image. However, phenomena such as“color deviation” and “granular quality” are an adverse image effectpeculiar to an ink jet printing apparatus. Thus, the present inventioncan be particularly effectively used when being used to an ink jetprinting apparatus. However, it is clear from the above description thatthe present invention also can be applied to a color conversionprocessing when a monochrome image is printed by an electro-photographictype printing apparatus using toner as color material.

Still Another Embodiment

The scope of the present invention also includes a configuration wherean apparatus or a computer in a system connected with various devices toallow the devices to realize the respective functions of the aboveembodiments is supplied with a program code of the software shown inFIG. 7 and FIG. 12 for realizing the above functions of the embodimentsso that the present invention is practiced by operating the respectivedevices in accordance with the program stored in the system or thecomputer of the apparatus (CPU or MPU).

In this case, the program code of the software will realize theabove-described functions of the embodiments. The program code itselfand a means for supplying the program code to the computer (e.g., astorage medium storing this program code) constitute the presentinvention.

Storage media storing the program code include, for example, floppy disc(registered mark), hard disc, optical disc, magnetooptical disc, CD-ROM,magnetic tape, nonvolatile memory card, and ROM.

Furthermore, by executing the program code supplied to the computer, theabove-described function of the embodiments is realized and this programcode is included in embodiments of the present invention even when theabove-described function of the embodiments is realized by thecooperation by an OS (operating system) in which the program code runsin the computer or another application software.

Furthermore, the present invention also includes a configuration where asupplied program code is stored in a function expansion board of acomputer or a memory included in a function expansion unit connected tothe computer and then a CPU included in the function expansion board orthe function storage unit for example performs, based on an instructionby the program code, a part or the entirety of an actual processing torealize the above-described function of the embodiments.

The present invention has been described in detail with respect topreferred embodiments, and it will now be apparent from the foregoing tothose skilled in the art that changes and modifications may be madewithout departing from the invention in its broader aspect, and it isthe intention, therefore, in the apparent claims to cover all suchchanges.

This application claims priority from Japanese Patent Application No.2005-118227 filed Apr. 15, 2005, which is hereby incorporated byreference herein.

1. An image processing apparatus comprising: color conversion means forconverting R, G, B signals into a plurality of ink color signalscorresponding to amounts of a plurality of color inks to be used, theplurality of color inks including achromatic color ink capable of beingused for printing a monochrome image, wherein the color conversion meansconverts the R, G, B signals into the plurality of ink color signals byusing a color conversion table that defines a correspondence relationbetween combinations of the R, G, B signals, which include combinationsof the R, G, B signals values of which are the same as each other andcombinations of the R, G, B signals values of which are not the same aseach other, and combinations of the plurality of ink color signals, sothat the achromatic color ink is used in all of a color reproductionregion which is reproducible with the plurality of color inks, andwherein the color conversion table defines the correspondence relationso that the amount of the achromatic color ink to be used is larger thanan amount of a chromatic color ink to be used in all of the colorreproduction region.
 2. An image processing apparatus comprising:setting means for setting a monochrome mode; and conversion means forconverting R, G, B signals that represent an image to be printed in themonochrome mode set by the setting means into a plurality of ink colorsignals corresponding to amounts of a plurality of color inks to beused, the plurality of color inks including achromatic color ink capableof being used for image printing in the monochrome mode, wherein theconversion means converts the R, G, B signals into the plurality of inkcolor signals by using a color conversion table that defines acorrespondence relation between combinations of the R, G, B signals,which include combinations of the R, G, B signals values of which arethe same as each other and combinations of the R, G, B signals values ofwhich are not the same as each other, and combinations of the pluralityof ink color signals, so that the achromatic color ink is used in all ofa color reproduction region which is reproducible with the plurality ofcolor inks, and wherein the color conversion table defines thecorrespondence relation so that the amount of the achromatic color inkto be used is larger than an amount of a chromatic color ink to be usedin all of the color reproduction region.
 3. An image processingapparatus comprising: setting means for setting a plurality of printmodes including monochrome and color modes; first conversion means forconverting R, G, B signals that represent an image to be printed in themonochrome mode into a plurality of ink color signals corresponding toamounts of a plurality of color inks to be used, the plurality of colorinks including achromatic color ink capable of being used for imageprinting in the monochrome mode, when the setting means sets themonochrome mode; and second conversion means for converting R, G, Bsignals that represent an image to be printed in the color mode into aplurality of ink color signals corresponding to amounts of a pluralityof color inks to be used, the plurality of color inks includingachromatic color ink capable of being used for image printing in thecolor mode, when the setting means sets the color mode, wherein thefirst conversion means converts the R, G, B signals into the pluralityof ink color signals by using a first color conversion table thatdefines a correspondence relation between combinations of the R, G, Bsignals, which include combinations of the R, G, B signals values ofwhich are the same as each other and combinations of the R, G, B signalsvalues of which are not the same as each other, and combinations of theplurality of ink color signals, so that the achromatic color ink is usedin all of a color reproduction region which is reproducible with theplurality of color inks, the second conversion means converts the R, G,B signals into the plurality of ink color signals by using a secondcolor conversion table that defines a correspondence relation betweencombinations of the R, G, B signals, which include combinations of theR, G, B signals values of which are the same as each other andcombinations of the R, G, B signals values of which are not the same aseach other, and combinations of the plurality of ink color signals, sothat the achromatic color ink is used in a part of a color reproductionregion which is reproducible with the plurality of color inks, and thereproduction region reproducible when using the first color conversiontable is smaller than the reproduction region reproducible when usingthe second color conversion table, and wherein the first and secondcolor conversion tables define the correspondence relation so that theamount of the achromatic color ink to be used is larger than an amountof a chromatic color ink to be used in all of the color reproductionregion, respectively.
 4. An image processing apparatus comprising: coloradjustment means for performing a color adjustment for a monochromeimage; and conversion means for converting R, G, B signals which isadjusted by the color adjustment means into a plurality of ink colorsignals corresponding to amounts of a plurality of color inks to beused, the plurality of color inks including achromatic color ink capableof being used for printing the monochrome image, wherein the conversionmeans converts the R, G, B signals into the plurality of ink colorsignals by using a color conversion table that defines a correspondencerelation between combinations of the R, G, B signals, which includecombinations of the R, G, B signals values of which are the same as eachother and combinations of the R, G, B signals values of which are notthe same as each other, and combinations of the plurality of ink colorsignals, so that the achromatic color ink is used in all of a colorreproduction region which is reproducible with the plurality of colorinks, and wherein the color conversion table defines the correspondencerelation so that the amount of the achromatic color ink to be used islarger than an amount of a chromatic color ink to be used in all of thecolor reproduction region.
 5. An image processing apparatus as claimedin claim 4, further comprising: setting means capable of setting colortones that differ from each other as color tones of the monochromeimage, wherein the color adjustment means performs the color adjustmentbased on a result of setting by the setting means.
 6. An imageprocessing apparatus as claimed in claim 4, wherein the color adjustmentmeans performs the color adjustment with a change of at least one of thecolor tone of the monochrome image, density of the monochrome image anda contrast of the monochrome image.
 7. An image processing apparatuscomprising: setting means for setting a monochrome mode; means forconverting R, G, B signals that represent an image to be printed in themonochrome mode into brightness signal in which R, G, B values are thesame as each other, when the monochrome mode is set by the settingmeans; color adjustment means for adjusting values of the R, G, Bsignals by using the brightness signal and a color adjustment parameter;and conversion means for converting R, G, B signals the values of whichthe color adjustment means adjusts into a plurality of ink color signalscorresponding to amounts of a plurality of color inks to be used, theplurality of color inks including achromatic color ink capable of beingused for image printing in the monochrome mode, wherein the conversionmeans converts the R, G, B signals into the plurality of ink colorsignals by using a color conversion table that defines a correspondencerelation between combinations of the R, G, B signals, which includecombinations of the R, G, B signals values of which are the same as eachother and combinations of the R, G, B signals values of which are notthe same as each other, and combinations of the plurality of ink colorsignals, so that the achromatic color ink is used in all of a colorreproduction region which is reproducible with the plurality of colorinks, and wherein the color conversion table defines the correspondencerelation so that the amount of the achromatic color ink to be used islarger than an amount of a chromatic color ink to be used in all of thecolor reproduction region.
 8. An image processing method comprising: acolor conversion step of converting R, G, B signals into a plurality ofink color signals corresponding to amounts of a plurality of color inksto be used, the plurality of color inks including achromatic color inkcapable of being used for printing a monochrome image, wherein the colorconversion step converts the R, G, B signals into the plurality of inkcolor signals by using a color conversion table that defines acorrespondence relation between combinations of the R, G, B signals,which include combinations of the R, G, B signals values of which arethe same as each other and combinations of the R, G, B signals values ofwhich are not the same as each other, and combinations of the pluralityof ink color signals, so that the achromatic color ink is used in all ofa color reproduction region which is reproducible with the plurality ofcolor inks, and wherein the color conversion table defines thecorrespondence relation so that the amount of the achromatic color inkto be used is larger than an amount of a chromatic color ink to be usedin all of the color reproduction region.
 9. An image processing methodcomprising: a setting step of setting a monochrome mode; and aconversion step of converting R, G, B signals that represent an image tobe printed in the monochrome mode set by the setting step into aplurality of ink color signals corresponding to amounts of a pluralityof color inks to be used, the plurality of color inks includingachromatic color ink capable of being used for image printing in themonochrome mode, wherein the conversion step converts the R, G, Bsignals into the plurality of ink color signals by using a colorconversion table that defines a correspondence relation betweencombinations of the R, G, B signals, which include combinations of theR, G, B signals values of which are the same as each other andcombinations of the R, G, B signals values of which are not the same aseach other, and combinations of the plurality of ink color signals, sothat the achromatic color ink is used in all of a color reproductionregion which is reproducible with the plurality of color inks, andwherein the color conversion table defines the correspondence relationso that the amount of the achromatic color ink to be used is larger thanan amount of a chromatic color ink to be used in all of the colorreproduction region.
 10. An image processing method comprising: a coloradjustment step of performing a color adjustment for a monochrome image;and a conversion step of converting R, G, B signals which are adjustedby the color adjustment step into a plurality of ink color signalscorresponding to amounts of a plurality of color inks to be used, theplurality of color inks including achromatic color ink capable of beingused for printing the monochrome image, wherein the conversion stepconverts the R, G, B signals into the plurality of ink color signals byusing a color conversion table that defines a correspondence relationbetween combinations of the R, G, B signals, which include combinationsof the R, G, B signals values of which are the same as each other andcombinations of the R, G, B signals values of which are not the same aseach other, and combinations of the plurality of ink color signals, sothat the achromatic color ink is used in all of a color reproductionregion which is reproducible with the plurality of color inks, andwherein the color conversion table defines the correspondence relationso that the amount of the achromatic color ink to be used is larger thanan amount of a chromatic color ink to be used in all of the colorreproduction region.